1. Field of the Invention
The present invention relates to an image forming apparatus and an electric appliance.
2. Description of the Related Art
A typical power control used in image forming apparatuses has three modes including a power-OFF mode, a stand-by mode, and a sleep mode.
In the power-OFF mode, a main power-supply switch is OFF and no power is supplied to the image forming apparatus, i.e., power consumption is zero.
In the stand-by mode, the main power-supply switch is ON and alternating current (AC) power is supplied to the image forming apparatus. Internally-used direct current (DC) power of, for example, 5 volts and 24 volts is generated from the AC power. The image forming apparatus is ready to perform an image-forming operation by driving by driving mechanism loads through a motor or a clutch with the generated DC power.
In the sleep mode, power is supplied to only a specific device that is a part of the image forming apparatus while the power supply to the other devices is cut off, which leads to lower power consumption. The image forming apparatus is switched to the sleep mode, for example, when a long period has passed since the last operation, or when a user makes a command to shift to the sleep mode via an operation key.
The specific device is connected to an output side of a return sensor and an external-device interface. When the specific device detects a state change about the return sensor or the external-device interface, the specific device starts a shift operation from the sleep mode to the stand-by mode. The specific device starts the shift operation, for example, when a user tries to perform a copy operation or an original reading operation, when a print command is received from an external device via a local area network (LAN) or a universal serial bus (USB), or when facsimile data is received. After the shift operation is completed, the image forming apparatus performs a print operation.
A control system of a conventional image forming apparatus is described below with reference to FIG. 8.
The conventional image forming apparatus includes an AC plug 1001, an AC switch 1002, a power-supply unit 1004, a mechanism control unit 1005, a group of mechanism loads 1006, a system control unit 1007, an image reading unit 1008, an image writing unit 1009, and a group of return sensors 1011. Reference numeral 1010 denotes external device.
When the AC switch 1002 is ON in a situation that the AC plug 1001 is connected to the AC outlet, the AC power is supplied to the power-supply unit 1004. The power-supply unit 1004 generates DC power including 24-V power and 5-V power, and supplies the DC power to the mechanism control unit 1005 and the system control unit 1007.
The mechanism control unit 1005 includes a central processing unit (CPU, not shown) and input/output control driver (I/O control driver, not shown). Upon receiving the DC power, the CPU activates and then performs driving of the mechanism loads 1006 in accordance with a predetermined image-forming sequence.
The image reading unit 1008 includes a lamp (not shown) that illuminates an original and a charge-coupled device (CCD, not shown). The image reading unit 1008 reads image data of the original by emitting a light to the original placed on an exposure glass and then receiving the light reflected from the original.
Upon receiving, as synchronizing with operation of the mechanism control unit 1005, the image data from the image reading unit 1008 as copy data, the system control unit 1007 processes the received image data and sends the processed image data to the image writing unit 1009.
The system control unit 1007 is connected to the external device 1010 via an interface such as a LAN or a USB. Upon receiving image data from the external device 1010 as print data, the system control unit 1007 enlarges/reduces the received image data or adjusts layout of the received image data, and sends the processed image data to the image writing unit 1009.
Upon receiving the image data from the system control unit 1007, the image writing unit 1009 switches ON/OFF of a laser diode based on the received image data, and emits a laser light from the laser diode to the photosensitive element, thereby forming an electrostatic latent image on a photosensitive element. After that, the electrostatic latent image on the photosensitive element is developed with toners, the developed toner image is transferred onto a recording medium, and the recording medium with the image is obtained.
In the following description, an explanation about a process of transferring the image on the photosensitive element onto the recording medium is omitted because the process is not a main subject of the present invention.
The power-supply unit 1004 includes two switches through which the DC voltage is output; one is for 24 volts and the other is for 5 volts. The switches turn ON/OFF based on a PON_ENG signal that is output by the system control unit 1007. The mechanism control unit 1005 receives the 5-V power and the 24-V power passed through the switches. The system control unit 1007 receives the DC power of 5 VE without passing through the switches.
The system control unit 1007 is connected to the return sensors 1011 including, for example, a power switch on an operation panel, a placed-original detecting sensor, or a platen-open/close detecting sensor. The system control unit 1007 monitors whether the user tries to operate the image forming apparatus during the sleep mode by constantly monitoring the return sensors 1011.
Moreover, the system control unit 1007 constantly monitors whether a print command has been received from the external device 1010 via the LAN or the USB or whether facsimile data has been received. When the system control unit 1007 detects a return factor from the return sensor 1011 or the external device 1010, the system control unit 1007 asserts the PON_ENG signal. In response to the asserted PON_ENG signal, the switches turn ON and the 5-V DC power and the 24-V DC power are supplied to the mechanism control unit 1005. Thus, the main system of the image forming apparatus activates.
When the system control unit 1007 detects that a long period has been passed since the last operation or a command to shift to the sleep mode has been received from a user using the operation key, the system control unit 1007 negates the PON_ENG signal. In response to the negated PON_ENG signal, the switches of the power-supply unit 1004 turn OFF and the power-supply unit 1004 stops supplying the 5-V power and the 24-V power to the mechanism control unit 1005. Thus, the image forming apparatus is shifted to the sleep mode.
In this manner, the image forming apparatus is automatically shifted to the sleep mode when a predetermined period has passed since the last operation, while automatically shifted to the stand-by mode when the signal from the return sensor monitored by the CPU is ON. This makes it possible to reduce the power consumption.
FIG. 9 is a timing chart for explaining operation performed by the conventional image forming apparatus.
When the AC switch 1002 turns ON, the AC power is supplied to the power-supply unit 1004, and the power-supply unit 1004 generates the 5-VE power from the AC power. When the system control unit 1007 receives the 5-VE power, the CPU of the system control unit 1007 activates and asserts the PON_ENG signal. The switches of the power-supply unit 1004 turn ON in response to the asserted PON_ENG signal, so that the 5-V power and the 24-V power are supplied to the mechanism control unit 1005. Thus, the image forming apparatus activates, i.e., is ready to operate.
Moreover, when it is determined with an internal timer of the system control unit 1007 that a long period has passed since the last operation, the system control unit 1007 negates the PON_ENG signal. In response to the negated PON_ENG signal, the power-supply unit 1004 stops supplying the 5-V power and the 24-V power. Thus, the image forming apparatus shifts to the sleep mode. During the sleep mode, the CPU of the system control unit 1007 constantly monitors the return sensor. When detecting that a user tries to operate the image forming apparatus, the system control unit 1007 asserts the PON_ENG signal again to activate the image forming apparatus.
Japanese Patent No. 3646958, which has been issued to the applicants of the present application, discloses an image forming apparatus in which ON/OFF of a power supply is controlled taking a state of an application function into consideration. More particularly, a power-supply control signal indicative whether the application function is running a job is sent to a power-supply control unit. The power-supply control unit controls ON/OFF of the power supply based on the power-control signal.
However, the conventional image forming apparatus described above needs certain power during the sleep mode, although less than that during the stand-by mode. In other words, there is room for reducing the power consumption.
Moreover, a main object of the conventional image forming apparatus disclosed in Japanese Patent No. 3646958 is not to reduce the power consumption during the image forming apparatus being in non-operation but to prevent data corruption due to a power breakdown that may happen during an application function being activated.